1. Field of the Invention
This invention relates to an improvement of an electronic device in which a pulse current flows in a circuit element such as a LED (light emitting diode) or thermistor.
2. Prior Art
One example of a conventional electronic device of this type is a pulse oximeter. The pulse oximeter generally uses an LED. In order to increase the quantity of light of the LED, it is essential to increase the current flowing therein. However, the steady application of large current to the LED suffers from the following difficulties: Heat generated by the LED, (1) lowers the efficiency of the LED itself, (2) thermally damages the LED, and (3) damages vital tissues adjacent to the LED. Accordingly, when a large current is applied to the LED, it should be in the form of a pulse. However, it should be noted that, if the circuit is modified so as to apply a large current, in the form of a pulse to an LED, which becomes out of order (i.e., allows a large current to continuously flow in the LED), then the circuit will suffer from the same difficulties.
As was described above, when the conventional pulse oximeter becomes out of order to cause current, to continuously flow in the LED, the latter is overheated. However, the conventional pulse oximeter has no means for eliminating or preventing this difficulty. Only the pulse oximeter with the LED has been described; however, the preceding description is applicable to electronic devices having a circuit element which is driven by a pulse current and which should be prevented from being overheated.